Fix sqlite3_stmt leak

They would eventually get freed with the connection, but this will free them sooner when an undisposed reader is finalized and the connection is still open.

Fixes #351

src/Microsoft.Data.Sqlite.Core/SqliteDataReader.cs

@@ -175,11 +175,6 @@ public override void Close()
         /// </param>
         protected override void Dispose(bool disposing)
         {
-            if (!disposing)
-            {
-                return;
-            }
-
             if (_stmt != null)
             {
                 _stmt.Dispose();
@@ -191,6 +186,11 @@ protected override void Dispose(bool disposing)
                 _stmtQueue.Dequeue().stmt.Dispose();
             }
 
+            if (!disposing)
+            {
+                return;
+            }
+
             _closed = true;
 
             if (_closeConnection)